P2‐323: Toll‐like receptor 9 stimulation via CpG ODN in a non‐human primate model of sporadic cerebral amyloid angiopathy

Abstract

Immunomodulation is a promising therapeutic approach for Alzheimer's disease (AD); however, major drawbacks are cerebral microhemorrhages associated with increased cerebral amyloid angiopathy (CAA) and excessive inflammation. Our initial findings indicate that stimulation of TLR9 signaling with CpG oligodeoxynucleotide (ODN) is effective against CAA without inducing toxicity in AD mouse models. To further assess potential human use of CpG ODN we advanced our studies using a well-established non-human primate model of sporadic CAA, squirrel monkey (Saimiri Boliviensis). Safety and efficacy assessment studies were first performed in young squirrel monkeys (SQM). Elderly female monkeys were subcutaneously injected either with the most effective and non-toxic dosages of the class B CpG ODN containing a primate specific immunostimulatory sequence or saline. Both age groups were subjected to behavioral testing. Plasma taken during the course of treatment was analyzed to identify immune responses and AD biomarkers. Fluidigm RT-PCR was used to evaluate mRNA levels of cytokines in SQM PBMCs. CpG ODN elevated the levels of various Th1/Th2 cytokines in plasma from old monkeys. Upregulation of cytokines in CpG ODN group was further confirmed by RT-PCR. Pre-treatment behavioral assessment in our aged monkeys demonstrated cognitive deficits on the Inhibitory Control of Behavior and Delayed Response tests. Age effect on cognitive abilities was observed as the young group performed with overall lower session error rates compared to old animals. Post-treatment behavioral testing in our aged monkeys is ongoing. Here we report the first pyroglutamate (pE3) immunohistochemistry of aged Saimiri Boliviensis. In addition to 6E10/4G8 Aß-positive plaques, pyroglutamate Aß-positive deposits in the form of CAA and parenchymal plaques were detected. Our preliminary biomarker analyses revealed a noticeable increase in Aß40, Aß42 and AßpE3 plasma levels in CpG ODN-treated group. Further longitudinal assessment of potential AD biomarkers is currently in progress. The presented studies represent the first trial of specifically targeting CAA in non-human primates. We hope that our research will validate this novel approach of immunomodulation as a safer method to successfully ameliorate AD related pathologies and provide critical data for potential clinical use of CpG ODN in AD patients.